drm/msm/dp: Implement hpd_notify()

The DisplayPort controller's hot-plug mechanism is based on pinmuxing a
physical signal on a GPIO pin into the controller. This is not always
possible, either because there aren't dedicated GPIOs available or
because the hot-plug signal is a virtual notification, in cases such as
USB Type-C.

For these cases, by implementing the hpd_notify() callback for the
DisplayPort controller's drm_bridge, a downstream drm_bridge
(next_bridge) can be used to track and signal the connection status
changes.

This makes it possible to use downstream drm_bridges such as
display-connector or any virtual mechanism, as long as they are
implemented as a drm_bridge.
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
[bjorn: Drop connector->fwnode assignment and dev from struct msm_dp]
Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/514410/
Link: https://lore.kernel.org/r/20221207220012.16529-10-quic_bjorande@quicinc.comSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dp/dp_display.c

@@ -1792,3 +1792,25 @@ void dp_bridge_hpd_disable(struct drm_bridge *bridge)
 
 	dp_display->internal_hpd = false;
 }
+
+void dp_bridge_hpd_notify(struct drm_bridge *bridge,
+			  enum drm_connector_status status)
+{
+	struct msm_dp_bridge *dp_bridge = to_dp_bridge(bridge);
+	struct msm_dp *dp_display = dp_bridge->dp_display;
+	struct dp_display_private *dp = container_of(dp_display, struct dp_display_private, dp_display);
+
+	/* Without next_bridge interrupts are handled by the DP core directly */
+	if (dp_display->internal_hpd)
+		return;
+
+	if (!dp->core_initialized) {
+		drm_dbg_dp(dp->drm_dev, "not initialized\n");
+		return;
+	}
+
+	if (!dp_display->is_connected && status == connector_status_connected)
+		dp_add_event(dp, EV_HPD_PLUG_INT, 0, 0);
+	else if (dp_display->is_connected && status == connector_status_disconnected)
+		dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 0);
+}

drivers/gpu/drm/msm/dp/dp_drm.c

@@ -104,6 +104,7 @@ static const struct drm_bridge_funcs dp_bridge_ops = {
 	.atomic_check = dp_bridge_atomic_check,
 	.hpd_enable   = dp_bridge_hpd_enable,
 	.hpd_disable  = dp_bridge_hpd_disable,
+	.hpd_notify   = dp_bridge_hpd_notify,
 };
 
 struct drm_bridge *dp_bridge_init(struct msm_dp *dp_display, struct drm_device *dev,

drivers/gpu/drm/msm/dp/dp_drm.h

@@ -34,5 +34,7 @@ void dp_bridge_mode_set(struct drm_bridge *drm_bridge,
 			const struct drm_display_mode *adjusted_mode);
 void dp_bridge_hpd_enable(struct drm_bridge *bridge);
 void dp_bridge_hpd_disable(struct drm_bridge *bridge);
+void dp_bridge_hpd_notify(struct drm_bridge *bridge,
+			  enum drm_connector_status status);
 
 #endif /* _DP_DRM_H_ */